I just let my cucumbers go until they reach the greenhouse roof, and then I fix either horizontal canes along the greenhouse ridges, or supports made of old tights joined together and stretched an tied along the apex of the roof. When said plant has romped its way from the back of the greenhouse and is heading out of the door at the front I nip out the growing tip of the leader. Other than that I let them do what they please and I always get a fantastic crop. The only tip I can give that might save your plants is to plant them slightly proud of the compost when you put them in, and always water from the bottom. They have a nasty habit of waving "bye bye" very rapidly if they get wet around the stem, as they are prone to stem rot.